1. Field of the Invention
The present invention relates to a system for contracting bit map image data, and more particularly, to a bit map image data contracting system which allows interactive correction of an image that has been brought out of shape when the bit map image data are contracted at a certain magnification on an apparatus operating in a computer graphics application.
2. Description of the Related Art
Apparatuses operating in a computer graphics application, such as CAD (Computer-Aided Design) systems, employ many displayed icons which are graphics representations of various functions that are required for the user to draw figures on a display screen. When an icon displayed on the display screen is indicated by a mouse pointer, for example, the function assigned to the icon is performed. These icons are composed of bit map image data. Icons are carried by the CAD systems themselves, and, in addition, some customized icons are uniquely generated by users.
In an apparatus operating in a computer graphics application, the reduced size of an icon or icons may be required when the version of an existing program run by the apparatus is changed. For example, such a reduction in the size of an icon or icons may be either necessary when the increase of the number of icons which are simultaneously displayed on the display screen is required, or necessitated in view of a screen display arrangement, or for reasons of the system. An icon composed of bit map image data can be reduced in size or contracted by appropriately decimating dot data according to the contraction ratio.
FIGS. 1(A) and 1(B) of the accompanying drawings show a conventional method of contacting bit map image data. FIG. 1(A) shows an original representation 2 of bit map image data having an original size 8.times.8 dots. FIG. 1(B) illustrates a contracted representation 4 of contracted bit map image data. In FIGS. 1(A) and 1(B), when displayed on a display unit, white pixels or dots in the square pixels in the original representation 2 and the contracted representation 4 are recognized as white pixels, and hatched pixels or dots which represent figures are recognized as black pixels. The data of the white pixels are of a value "0" and the data of the hatched pixels are of a value "1". In the illustrated example, the bit map image data are contracted only in the horizontal direction. However, bit map image data are usually contracted in both the horizontal and vertical directions.
The original representation 2 includes pixels marked with "X", and two pixel columns including these marked are to be decimated from the bit map image data. When the two pixel columns are decimated from the original representation 2, the original representation 2 is converted into the contracted representation 4 whose horizontal dimension has been reduced at a contraction ratio of 75%. The bit map image data can be contracted to a desired size by setting the number of rows or columns of pixels to be decimated from the original representation 2 to a number depending on the contraction ratio.
Bit map image data representing an icon are expressed by a relatively small number of dots, and a vertical or horizontal line segment thereof may be drawn with a minimum dot width. If such a line segment happens to coincide with a row or column of pixels to be decimated from the original representation 2, then the line segment is eliminated in its entirety, and the bit map image data may sometimes be contracted to a shape dissimilar to the original shape or entirely different from the image of the original representation 2. For example, if one of the columns of pixels to be decimated in FIG. 1(A) is shifted one dot to the left or right, then one of the vertical line segments represented by hatched square pixels will be decimated as a whole, with the result that the contracted bit map image data represent a C-shaped figure. When such a problem arises, it has heretofore been necessary to modify the contracted figure with an editor or the like.
The modification does not cause a substantial problem if the number of bit map image data is small. However, if icons are provided in such a hierarchical arrangement that when one icon is opened, a next icon appears, then the number of icons used may reach up to several hundreds, and it will be very laborious to rewrite the icons one by one manually. Since many users generate their own icons using the customizing function, it is desirable that these customized icons be contracted to images which remain essentially the same as the image of the original representation 2.